1. Technical Field
The present invention relates to sealing leaks in and structurally repairing pipes and, more particularly, to a method and apparatus having utility in repairing and sealing leaks in pipelines that are substantially inaccessible to repair personnel. The present invention is described primarily for use in repairing sewer lines; however, it is to be understood that the invention has utility in the repair of substantially any pipeline, tunnel, conduit, shaft, etc.
2. Description of the Prior Art
Approximately half of the effluent treated at waste water treatment plants in the United States is the result of unintended infiltration and inflow into sewer pipe lines. In addition, as much as thirty percent of water and twenty-five percent of natural gas entering respective water and gas distribution systems is unaccounted for, presumably because of leakage from distribution pipelines. The age of many distribution systems assures that the problem will not disappear, yet the cost of replacing an entire system is enormous and, in most cases, prohibitive. Accordingly, it is desirable to provide an inexpensive and efficient technique for repairing leaks in existing pipelines. Several known approaches to the problem are outlined below.
Excavation is very commonly used to provide access to pipeline leaks so that the damaged section may be replaced or repaired in situ. However, excavation is extremely expensive and is disruptive of surface activities such as pedestrian and vehicular traffic. Moreover, in many instances it is impossible to reach the damaged pipe because numerous other pipes and conduits are disposed between the damaged pipe and the ground surface.
In another pipe repair approach, a lining of polymer and felt is disposed within the defective pipe section and cured in place. For example, see U.S. Pat. Nos. 4,064,211 and 4,581,247. The result is a new structural line that prevents infiltration of fluids into the pipe. Although functionally satisfactory for some applications, this approach tends to be expensive and also requires that the defective pipe section be removed from service during the curing process which lasts in excess of twenty-four hours. Moreover, this technique requires that the entire pipeline between two access openings (i.e., manholes) be relined, resulting in gross inefficiency when only a short section of pipe requires repair.
A technique known as slip lining, also relatively expensive, involves relining an entire pipe section between access openings with a rigid structural liner. In addition to being inefficient for short sections of defective pipe, this technique requires excavation in order to attach the repaired section to lateral service lines.
Various internal seals are effectively utilized for certain types of pipe defects but require human access within the defective pipe section and are therefore limited to pipes having inside diameters of at least twenty-four inches.
Another prior art seal unit takes the form of arcuate plates having foam glued to their convex surfaces and jointed by hinges. The seal is collapsed to a figure-eight and moved within the pipe to the location to be repaired, where jacks are then employed to force the plates into contact with the pipe wall. Such units have been known to collapse unexpectedly, thereby removing the repair seal while presenting a blockage inside the pipeline.
Still a further seal arrangement, sold under the trade name SNAP-LOCK, employs a stainless steel longitudinally slit tube that is partially rolled into a spiral to facilitate passage through a pipeline. A foam material is glued onto the outer surface of the tube which is disposed about a remoately actuated inflatable bag. When the tube is positioned in alignment with the defect in the pipe, as viewed by television monitoring, the bag is inflated to unroll the tube so that the foam is compressed against the pipe wall. The tube is biased to unroll so that it remains in place after the air bag is deflated. This apparatus has proven difficult to install because of friction introduced by the foam material coating, that acts in opposition to the unrolling of the tube when the bag is inflated. On the other hand, if foam having a lower coefficient of friction is employed, the foam tends to slide along the pipe wall and, accordingly, does not adequately seal the leak.
A somewhat different approach is found in U.S. Pat. No. 3,261,374 (Anderson et al) wherein a heat-reactive plastic tube is expanded by the application of thermal energy so as to tightly fit against the defective pipe wall. Immediately prior to insertion of the tube into the pipe, the exterior of the tube is coated with a tacky material that maintains the tube adhered to the pipe wall after the expanded tube is cooled. The application of the tacky substance at the repair site is inconvenient at best, and is also time-consuming and expensive. Moreover, the tacky substance renders the tubing difficult to transport through the pipeline.